The present invention relates to monitoring arrangements and more particularly to such monitoring arrangements utilised with regard to rotating components such as turbine blade assemblies in a gas turbine engine.
It is important to be able to monitor components such as rotating blade assemblies in order to determine distortion and deflection in that component during operational use.
It will be understood that rotating components will be subject to varying stresses and strains during use and therefore generally each of these components will distort and become displaced. A particular problem with respect to turbine blade assemblies in gas turbine engines is a so called blade-off situation where a blade becomes fully or partially detached or at least displaced causing rubbing with other components within the assembly. In such circumstances it is important to determine the varying distortions and displacements which precede such blade off situations in order that they can be avoided.
Previously the main means of monitoring a rotating component has been by simple observation. Thus, a camera will be mounted in an appropriate position relative to the rotating component in order to record its motion and then through subsequent replaying and observation distortions and displacements noted in the rotating component. It will be understood in order to highlight distortions and displacements typically a high intensity laser or other illumination source has been used in order to give high brightness and a narrow bandwidth light response. In such circumstances utilising a specially modified high-speed digital camera that generally only accepts or is biased towards the laser light bandwidth and rejects the background light emitted background it is possible to improve the accuracy of observations.
However, there are still particular problems from background or environmental light obscuring observations. This background light may be as a result of plasmas, arcs, flames and explosions typical in a gas turbine engine. It will also be understood that there may be dust or other particles which act as reflectors and so may further blind the camera in terms of its observational capacity.
In view of the above, previous methods are generally poor, and at least far from ideal, as it requires a high illumination level of light in order to indiscriminately penetrate the environmental pollution, that is to say, fog, dust, smoke, metallic and paint particles, soot, flames, water vapour, mist in the region in front of a rotating component such as a blade assembly in a gas turbine engine. However, a high illumination level can itself “blind” the camera by reflective light scatter from these particles. It would also be understood that there is lack of consistency in that the level of pollution which could cause camera blinding scatter may vary dependant upon operational state. In such circumstances it is not easy to provide any precision with regard to measuring displacement and distortion in the rotating component. Proposed attachment of high brightness devices to the rotating component will generally be unsatisfactory in that the device, that is to say a powered illumination source may be subject to breakage, provision of the device itself including its power supply will add to weight and therefore be intrusive with respect to a true response and may have limited effect upon the camera overall illumination.